Low power, battery operated environments present an environment where electronics are more susceptible to humidity-induced environmental changes. A particularly acute need exists in commercial utility meters such as natural gas meters, water meters or electric meters. Such applications are exposed to temperature extremes of -40.degree. F. to 160.degree. F., in varying humidity conditions, and sometimes even immersed in water. Additionally, battery life in such commercial utility meters must extend to 10 or more years in certain applications. Given the low power environment inherent in extended battery life applications, the electronics are configured to periodically awaken from an ultra-low power idle state for processing.
The electronics are implemented on printed circuit boards having electronic components such as integrated circuits, crystals, inductors, batteries resistors, capacitors, diodes, transistors, switches and sockets. Each of these components has leads which mount to the surface of the printed circuit board, as in surface mount applications, or extend through the circuit board as in traditional thru-hole applications. Conformal coatings for printed electrical circuit boards, including the components and the associated leads, and techniques for coating the same have been used to prevent corrosion and shorting from exposure to humid conditions. However, many conformal coatings, in particular, the widely used acrylic-based coatings, often delaminate or pull away from the corners of leads and boards and develop cracks which wick moisture during temperature and humidity cycles. These cracks and areas of delamination form pockets which may entrap water and dissolve and/or disassociate contaminants confined therein. These contaminants may eventually form dendritic growths between component leads, which lead to shorts, excessive power consumption and board malfunctions. These problems are exacerbated in low power, battery operated environments where moisture and dendritic formations between leads project a relatively low impedance, with respect to the high impedance battery application.
Therefore, there remains a need for a conformal coating for printed circuit boards which will provide moisture and corrosion resistance for the printed circuit boards and the components mounted thereto without cracking or delaminating.